Downgrade your iCloud storage
You can choose a lower-tier storage plan to replace your higher-tier plan (for example, a 10 GB plan to replace a 20 GB plan). The downgrade takes effect one year after your storage upgrade was initially purchased.
On your iOS device
Go to Settings > iCloud > Storage & Backup, then tap Change Storage Plan.
Tap Downgrade Options, then choose the storage plan you’d like to have.
On your Mac
Open iCloud preferences, then click Manage.
Click Change Storage Plan (in the upper right).
Click Downgrade Options, then choose the storage plan you’d like to have.
On your Windows computer
Open the iCloud Control Panel, then click Manage.
Click Change Storage Plan, then click Downgrade Options.
Select the storage plan you’d like to have.